> From: Liu, Yi L <yi.l....@intel.com> > Sent: Monday, June 29, 2020 8:23 PM > > Hi Stefan, > > > From: Stefan Hajnoczi <stefa...@gmail.com> > > Sent: Monday, June 29, 2020 5:25 PM > > > > On Wed, Jun 24, 2020 at 01:55:15AM -0700, Liu Yi L wrote: > > > +/* > > > + * struct iommu_nesting_info - Information for nesting-capable IOMMU. > > > + * user space should check it before using > > > + * nesting capability. > > > + * > > > + * @size: size of the whole structure > > > + * @format: PASID table entry format, the same definition with > > > + * @format of struct iommu_gpasid_bind_data. > > > + * @features: supported nesting features. > > > + * @flags: currently reserved for future extension. > > > + * @data: vendor specific cap info. > > > + * > > > + * +---------------+----------------------------------------------------+ > > > + * | feature | Notes | > > > + * > > > +===============+=============================================== > ==== > > =+ > > > + * | SYSWIDE_PASID | Kernel manages PASID in system wide, PASIDs > used | > > > + * | | in the system should be allocated by host kernel | > > > + * +---------------+----------------------------------------------------+ > > > + * | BIND_PGTBL | bind page tables to host PASID, the PASID could | > > > + * | | either be a host PASID passed in bind request or | > > > + * | | default PASIDs (e.g. default PASID of aux-domain) | > > > + * +---------------+----------------------------------------------------+ > > > + * | CACHE_INVLD | mandatory feature for nesting capable IOMMU > | > > > + * +---------------+----------------------------------------------------+ > > > > This feature description is vague about what CACHE_INVLD does and how > to > > use it. If I understand correctly, the presence of this feature means > > that VFIO_IOMMU_NESTING_OP_CACHE_INVLD must be used? > > > > The same kind of clarification could be done for SYSWIDE_PASID and > > BIND_PGTBL too. > > For SYSWIDE_PASID and BIND_PGTBL, yes, presence of the feature bit > means must use. So the two are requirements to user space if it wants > to setup nesting. While for CACHE_INVLD, it's kind of availability > here. How about removing CACHE_INVLD as presence of BIND_PGTBL should > indicates support of CACHE_INVLD? >
So far this assumption is correct but it may not be true when thinking forward. For example, a vendor might find a way to allow the owner of 1st-level page table to directly invalidate cache w/o going through host IOMMU driver. From this angle I feel explicitly reporting this capability is more robust. Regarding to the description, what about below? -- SYSWIDE_PASID: PASIDs are managed in system-wide, instead of per device. When a device is assigned to userspace or VM, proper uAPI (provided by userspace driver framework, e.g. VFIO) must be used to allocate/free PASIDs for the assigned device. BIND_PGTBL: The owner of the first-level/stage-1 page table must explicitly bind the page table to associated PASID (either the one specified in bind request or the default PASID of the iommu domain), through VFIO_IOMMU _NESTING_OP CACHE_INVLD: The owner of the first-level/stage-1 page table must explicitly invalidate the IOMMU cache through VFIO_IOMMU_NESTING_OP, according to vendor-specific requirement when changing the page table. -- Thanks Kevin
